Bundle listener that writes out Java Flight Recorder events to track startup time of bundles.

For the write-up, see https://alblue.bandlem.com/2020/02/jfr-bundle-listener.html

This is derived from the talk given at https://alblue.bandlem.com/2016/10/eclipsecon-books.html but at which point I was not able to open-source the code other than that listed in the presentation. Due to changes in the JFR API since being made public, and the fact that JFR is available by default in Java 11, this code now makes sense as a standalone open-source library.

The bundle provides a synchronous BundleListener which will listen to (subsequent) bundles started in the platform and record their being time of starting and the end time of started, and record the events via Java Flight Recorder.

The bundle needs to be installed into the OSGi framework or Eclipse platform, and started, prior to other bundles being started. They typical way to do this is to set up the bundle with a startLevel of 1, since frameworks that have the start level mechanism provide a way to start up bundles in specific orders. Alternatively, the framework may start up bundles in an order listed on the configuration of which bundles are installed. Consult your application's documentation for more details.

To run a Java application and enable JFR recording, the following flags are required on the JVM:

$ java -XX:StartFlightRecording=filename=/tmp/dump.jfr,dumponexit=true,disk=true ...

This will start the flight recorder as soon as the JVM is launched, writing out to /tmp/dump.jfr, and flushing upon exit. The file can then be loaded into Java Mission Control, or post-processed with the JFRFlameGraph executable to produce stacks that can be consumed by FlameGraph:

$ java -jar JFRBundleListener.jar /tmp/dump.jfr /tmp/stacks.txt
$ git clone https://github.com/brendangregg/FlameGraph
$ FlameGraph/flamegraph.pl --hash --countname ms < /tmp/stacks.txt > /tmp/bundles.svg

This will result in images that look like:

More information about flame graphs can be found on Brendan Gregg's page at http://www.brendangregg.com/flamegraphs.html

The ordering of the pillars is alphabetical, and does not indicate start order. However, higher layers start (and finish) before lower layers. In this case, the start-up time for org.eclipse.ui.trace (963ms) is almost completely taken up by the start-up time for org.eclipse.core.runtime (953ms), which in turn is taken up by org.eclipse.core.contenttype (883ms) that depends upon org.eclipse.equinox.registry (877ms). Together, this accounts for a little less than 25% of the start-up time of a general Eclipse instance.

The bundles are split by thread; the Start-Level thread is the name given to Equinox as it starts up; the main thread is used for most other start-up purposes. Threads with Worker-n are largely created in the background on separate threads, so themselves are unlikely to cause too much delay to start-up.

Since the SVG is interactive, the items can be clicked and zoomed in, which can help expand issues further.